The proposed activity of the high-voltage electron microscope facility in Boulder, Colorado will continue a pattern similar to that evolved during the first grant period. Microscope time will be equally shared between outside users (extramural projects) and faculty of the MCD Biology Department (intramural projects). Continued and more systematic use will be made of the stereoscopy of thick sections and whole cultured cells, with anticipated benefits for three-dimensional reconstruction. Selective staining will be explored more systematically to help identify large parts of intra-cellular systems and to isolate these from the complexity depicted in thick specimen micrographs. Frozen and frozen-dried specimens will be examined with the purpose of distinguishing artifacts in specimens prepared by the more conventional techniques of chemical fixation and alcohol dehydration. Ultrastructure details will be viewed within the limitations imposed by available resolving power and beam-induced radiation damage. Several technological and operational improvements of the installation will be carried out. The development of an energy filter for the reduction of chromatic aberrations will be pursued.